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The duplex stainless steel UNS S32205 was plasma nitrided at 380 °C for 10 h using a gas mixture of 25% N2-75% H2. The thickness of the nitrided layer was 4.5 ± 0.5 μm, composed mainly of nitrogen-expanded austenite and iron nitrides precipitates. There was an increase in surface hardness around 2.6 and 3.8 times in the nitrided layer formed on the austenite and the ferrite phases, respectively, in relation to the untreated samples. The surface texture parameters skewness (Ssk), maximum peak height (Sp) and texture aspect ratio (Str) were the most appropriate parameters for studying the topography changes after treatment. An improvement in the localized corrosion properties after the nitriding treatment was revealed by the cyclic polarization curves. The nitrided samples showed higher pitting corrosion and repassivation potentials compared to the untreated material. The ferritic phases and grain boundaries were more susceptible to corrosion in the nitrided samples. The potentiodynamic curves of the nitrided samples exhibited a hillside on the passive-to-transpassive transition. This feature was already observed by other researchers, but it has not been well investigated. Potentiostatic studies demonstrated that metastable pitting took place on this transition.

Resumo Objetivo Análise biomecânica comparativa da resistência da fixação tibial para reconstrução ligamentar com parafuso de interferência, comparada com parafuso do tipo poste com arruela, e com fixação associada entre os métodos (fixação híbrida). Métodos Foram utilizados 54 corpos de prova (tíbia suína e tendão digital bovino), que foram divididos em 3 grupos com tipos de fixação semelhantes àqueles utilizados na reconstrução do ligamento cruzado anterior: 1) fixação com parafuso de interferência; 2) fixação com parafuso do tipo poste com arruela dentada sobre nó e fios de sutura; e 3) fixação com parafuso do tipo poste com arruela combinada com parafuso de interferência (fixação híbrida). Os testes foram realizados por meio de ensaios biomecânicos de tração tipo pull-out para determinação da rigidez e carga para falha (yield load) do sistema. Resultados O grupo com fixação híbrida apresentou maior rigidez final (59,10 ± 3,45 N/mm) do que os demais grupos (p Conclusão A fixação híbrida apresentou vantagens biomecânicas com relação ao sistema de fixação do enxerto de flexor digital bovino em tíbia suína durante os ensaios de tração.

Corrosion resistance of plasma carburized AISI 420 martensitic stainless steel was evaluated by cyclic polarization test in 3.5% NaCl solution. Two distinct treatment groups were studied with the purpose of evaluating the influence of the carburizing temperature and time on the corrosion behavior of treated material (one at 350–500 °C temperature range for 8, and 12 h times; and other one at 400 °C for 12–48 h time range, and at 450 °C for 4–16 h time range). To support the discussions on electrochemical test results, microstructural characterization was carried out using metallographic analysis and XRD techniques. Microstructural characterization results show that low temperature and short time treatments produce outer layer composed by α′C and Fe3C phases. High temperature and/or long time treatments promote outer layer Cr7C3 and Cr23C6 phases precipitation. Corrosion test results show improved carburized samples resistance, which is related to chromium-carbides precipitation-free outer layer formation. The Cr-carbides formation promotes a reduction on carburized samples corrosion resistance due to depletion of Cr in the solid solution of carburized layer. Finally, by confronting the behavior of untreated and carburized samples, it is verified the potentialities of the low-temperature plasma carburizing to enhance the corrosion resistance of AISI 420 MSS.

Duplex surface treatments involving plasma nitriding (PN) followed by laser hardening (LH) were performed in this work on grade 450 compacted graphite iron (CGI) to investigate the effects of PN duration (1 and 3 h) and LH power (400, 449, and 514 W) on microstructure evolution, nitrogen profile, and hardening depth of CGI. X-ray diffraction (XRD) phase analysis indicated a reduction in and partial decomposition of e and γ’ nitrides corresponding to an increase in laser power. The existence of a new nitrogen-rich austenitic phase—FeN0.076—was observed along with the identification of certain iron oxides. The proposed duplex treatment of CGI was found to facilitate the establishment of duplex layers with higher surface hardness (826–951 HK 0.05) and greater hardening depths (300–750 μm). Additionally, a reduction in the hardness gradient was observed between the surface and substrate. This affords a major advantage in applications involving operations on mechanical components.

The reactions that can occur on organic materials treated in plasma enviorement are strongly affected by surface temperature, thus the sharp determination of this variable is extremely important to process control. In situ temperature measurements are often employed; however, the measured point is generally under the treated surface. If in metallic materials the high thermal conductivity minimizes this problem, in non-metallic materials processing it becomes important, because its thermal resistivity besides a high sensibility to small temperature variations. The present work uses a simulation tool to extract thermal data on Ar+O2 RF plasma processing of Stearic Acid. Experimental data were obtained by thermocouples placed inside the samples. The extrapolation of surface temperature was performed by numerical simulation with Autodesk CFD software v.15.1. Results show that the temperature of the surface reaches values higher than the ones measured inside the sample holder. This difference of temperature is in good agreement with the visual observation of the phase transformations in the treated material, showing a simple and valuable tool to better control of plasma treatments.

The UNS S32750 super duplex stainless steel (SDSS) was low temperature plasma nitrided at 350 °C and 400 °C for 4 h. Pitting and crevice corrosion resistance was evaluated using electrochemical techniques in a NaCl neutral solution. Nitriding treatments resulted in increased in hardness, general corrosion resistance and in the passive layer breakdown potential. Regarding crevice corrosion tests, the nitrided surfaces showed lower current densities during the potentiostatic polarization and lower corrosion depths when compared to the untreated surface. The nitrogen played a fundamental role in the passivation behavior and in the susceptibility to repassivation of localized corrosion.

The purposes of this study were to evaluate the effects of different preactivation bends on the force system and the mechanical stresses of beta-titanium T-loop orthodontic springs. A tridimensional T-loop spring finite element model was built aiming to obtain reactive forces and moments in the three directions (x, y and z) as well as the moment–force ratios (M/F) for the sagittal and occlusal planes considering different gable bends. Using a transducer designed to measure forces in the x- and y-axis and moment around the z-axis, experimental tests were performed to validate the numerical analysis. It was observed that F x increases as the angle between extremities increases. The F x magnitude changed from 0.2 to 2.0 N. F y forces presented very low magnitude while in z direction they were null. In the sagittal plane, decreasing the gable bends increases the M/F ratio. On the other hand, in the occlusal plane, no change in the M/F ratio values was observed with the variation of the gable bends. The results obtained from the analyses showed that the M/F ratio presented different values because of different preactivation bends formed between alpha and beta extremities, consequently different types of dental movement can be produced. In the occlusal plane, no movement tendency was observed while in the sagittal plane there was a movement tendency to produce uncontrolled tipping, controlled tipping, translation and finally root correction. Translation tendency was observed during deactivation starting at 5.0 mm without crown rotation.

The properties of the “nitrogen expanded ferrite” or αN phase have been scarcely studied to date. This phase was obtained here on a super ferritic stainless steel (SFSS) by plasma immersion ion implantation (PIII), which is a suitable technique to produce near to surface modifications on the Fe Cr alloys due to the control of energy delivered to the surface. The UNS S44400 SFSS, a special alloy developed for extreme corrosion environments, was nitrided by PIII at temperatures from 300 °C to 400 °C resulting in the αN phase as the main product of nitriding on the modified layer. The surface hardness measured by nanoindentation was investigated in the modified layers, reaching up to 3.5 times (the 400 °C condition) the hardness value presented by the untreated sample. The nitrided surfaces also presented improved corrosion resistance in comparison to the untreated sample, inferred by potentiodynamic polarization tests in NaCl electrolyte. This was evidenced by increased corrosion and pitting potentials (Ecorr and Ep, respectively) and decreased corrosion and passive current densities (icorr and ip, respectively). Moreover, through of the analysis in the polarization curves of the nitrided samples, a greater stability of the passive layer and repassivation processes were identified. The best corrosion resistance was obtained for the sample nitrided at 300 °C, which presented the greatest reduction in icorr and ip (6.6 μA/cm2 and 43 μA/cm2, respectively) and increase in Ecorr and Ep (108 mV and 214 mV, respectively), when compared to the untreated sample. In both untreated and nitrided samples, the addition of Nb and Ti in this alloy to prevent intergranular corrosion led to the formation of N- Ti-Nb-Mo precipitates that acted as initiators of pitting corrosion.

This work presents the application of Solution Heat Treatment after Plasma Nitriding (SHTPN) followed by requenching and tempering to the AISI 409 stainless steel aiming to increase hardness with no compromise of corrosion resistance. The SHTPN process consists of applying solution treatment to a previously plasma nitrided surface, promoting the dissolution of nitrides and the formation of a nitrogen-rich layer, in which nitrogen is in solid solution. When applied to ferritic stainless steels, SHTPN allows the obtention of a high‑nitrogen martensitic layer. It is presented an evaluation of the effects of requenching (from 950 and 1050 °C) and tempering (at 250, 450 and 650 °C) processes on the microstructure, hardness, and corrosion resistance of the nitrided layer of samples previously treated by SHTPN. Corrosion resistance was assessed through cyclic potentiodynamic polarization tests carried out in NaCl 0.5 mol/L, according to ASTM G150 . Optical and scanning electron microscopy, wavelength dispersive spectroscopy, and X-ray diffraction were applied to microstructural and phase characterization. Surface hardening was evaluated by Vickers microhardness tests. Results have shown that the requenching of SHTPN samples promoted a deepening of the nitrided layer and microstructure refinement. The process with requenching from 1050 °C and tempering at 250 °C led to increasing both hardness and corrosion resistance. These results confirmed that nitrogen in solid solution increases the hardness and the potential for pit nucleation in the AISI 409 stainless steel.

Compacted graphite iron is an interesting material class for automotive applications. CGI-450 grade cast iron was subjected to various surface treatments: plasma nitriding (PN), laser hardening (LH), and PN followed by LH (PN+LH). The resulting tribological behaviors were evaluated by means of linear scratch testing under progressive loading (40–70 and 70–95 N). The PN+LH treatment yielded the lowest friction coefficient and shallowest scratching. In this case, the outermost layer was composed of oxide phases (Fe2O3 and Fe3O4), underlain by a compound layer (oxides + nitrides + martensite) and a high-resistance martensitic layer with accompanying nitrides and carbides. These underlying layers provided high load capacity for the external layers, allowing them to function as solid lubricants.

Plasma surface cleaning is an alternative process that aims at the fully removal of organic contaminants on several kinds of materials. Despite its advantages, there are still lacks on the comprehension of the complex relations between plasma-generated species and organic molecules during plasma cleaning. In the present work, a linear alkane (hexatriacontane - C36H74), used as a contaminant model, was exposed to an Argon radiofrequency (RF) inductively coupled plasma (ICP). The by-products from degradation were monitored by optical emission spectroscopy (OES) and residual gas analysis (RGA), to identify the influence of sample positioning on E and H discharge modes regions. The exposition to H-mode discharge resulted in more intense and profuse emissions of C-H and C2 systems. RGA results show similar byproducts from degradation in both modes; however, the intensity from treatment in H-mode is largely greater. It was also observed that plasma etching in H-mode is enough to melt the sample, while E-type discharge leaves the surface of the sample apparently unchanged.

OBJECTIVE: A systematic review on nickel-titanium wires was performed. The strategy was focused on Entrez-PubMed-OLDMEDLINE, Scopus and BioMed Central from 1963 to 2008. METHODS: Papers in English and French describing the behavior of these wires and laboratorial methods to identify crystalline transformation were considered. A total of 29 papers were selected. RESULTS: Nickel-titanium wires show exceptional features in terms of elasticity and shape memory effects. However, clinical applications request a deeper knowledge of these properties in order to allow the professional to use them in a rational manner. In addition, the necessary information regarding each alloy often does not correspond to the information given by the manufacturer. Many alloys called "superelastic" do not present this effect; they just behave as less stiff alloys, with a larger springback if compared to the stainless steel wires. CONCLUSIONS: Laboratory tests are the only means to observe the real behavior of these materials, including temperature transition range (TTR) and applied tensions. However, it is also possible to determine in which TTR these alloys change the crystalline structure.

Austenitic stainless steels, although highly resistant to general corrosion, are susceptible to localized pitting or crevice corrosion. Corrosion resistance and mechanical properties could be enhanced by adding nitrogen to the alloy in solid solution. The methods currently in use involve fusion and solidification of the material, which may often be a deterrent, from the cost–benefit analysis stand point. In this article, the solution heat treatment after plasma nitriding (SHTPN) is presented as a new method to increase the surface nitrogen content in the solid state. The results obtained demonstrated the efficiency of this technique, by which the achieved thickness of the nitrided steel reaches up to 200 μm with 0.45 wt% of nitrogen.

As a general rule in powder injection molding (PIM), changes in processing parameters and powder characteristics (morphology, average size, surface area, and chemical composition) affect the sintering mechanism, causing changes in the microstructure and, consequently, in component performance. The current work investigates the influence of additions of different fractions of water-atomized to gas-atomized powders (0, 25, 50, 75, and 100%) on the corrosion resistance of injection molded 316L steel. In order to obtain a standard for comparison, an analysis of plated steel with similar composition was also performed. The corrosion investigation was carried out by electrochemical tests (potential vs time, Tafel and cyclic polarization) in a 3.5% salt solution medium. The tests took place at room temperature by employing computer controlled potenciostat/galvanostat equipment. The results presented are: open circuit potential, corrosion rate, pit density, pitting nucleation potential, and protection potential. The chemical and microstructure characterization was performed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray dispersive energy spectroscopy (EDS), optical emission spectroscopy and X-ray photoelectron spectroscopy (XPS). Although water atomized powders are generally thought as inferior regarding corrosion resistance mainly due to its higher oxygen content, the behavior of the analyzed samples do not greatly differ. Moreover the injection molded steel showed lower corrosion rate compared to the plated steel regardless its higher pit density.

Powder characteristics and manufacturing processes determine the microstructure, and therefore, the physical, chemical, and mechanical properties of sintered steels. In particular, porosity and corrosion resistance are intimately related, since the contact area between substrate and electrolyte significantly affects the corrosion resistance of sintered steels. This study addresses the effect of powder characteristics and pressing parameters on the microstructure and corrosion resistance of low-carbon sintered and sintered/plasma-nitrocarburized steel. The results indicated that the corrosion resistance increased with increasing density and decreasing specific surface area. Additionally, plasma-nitrocarburizing was highly effective in coating open pores of the material.

Plasma cleaning is a promising technology in surface treatments, despite technological interest its use is limited because its mechanisms still are not entirely understood. This work aims to evaluate how the applied power of an inductively coupled RF discharge at 13,56 MHz, with Ar and Ar+10%O2 atmospheres, affects its capabilities to etch an organic molecule. Mass variation rate was used as direct characterization of degradation process and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was performed to search for residual molecular modifications. Additionally, optical emission spectroscopy (OES) measurements were performed to monitor the offer of active species in the gaseous volume. In experimental conditions was possible attain mass reduction from sample, with higher mass loss rate when applied power is increased. Material characterization shows the possibility of attain a high etch rate, while no structural modifications were detected, if the temperature is controlled.

INTRODUCTION: The purpose of this study was to analyze the force system, moment-force ratios (M/F) and von Mises stresses in an orthodontic delta spring using a 3D finite element model. The M/F ratio produced by an orthodontic spring is related to the different types of tooth movement that are likely to occur in the sagittal and occlusal planes. METHODS: Analyses were performed using a 3D finite element model, and a data acquisition system was used to validate the numerical results. RESULTS: Reactive forces between 0.0 and 2.0 N were observed along the x-axis, while null values were observed along the y- and z-axes. The maximum activation that ensured geometric stability and mechanical stresses below the elastic limit of the material was 10.0 mm. CONCLUSION: The results indicate that a delta spring can provide (i) uncontrolled tipping for activation of less than 1.0 mm; (ii) controlled counterclockwise tipping for activation between 1.0 and 4.5 mm; (iii) translation for activation between 4.5 and 5.0 mm; and (iv) controlled clockwise tipping in the sagittal plane for activation between 5.0 and 10.0 mm. No tooth movement was observed in the occlusal plane for the M/F ratios observed.

The Response Surface Method (RSM) was employed to study the effect of the nitriding parameters on the corrosion resistance of a sintered steel of composition 3.8 Mn - 0.4 C - Fe (wt.%). Two atmospheres were used: 25% H 2 - 75% N 2 , and 1.25% CH 4 - 23.75% H 2 - 75% N 2 . For each atmosphere, samples were nitrided at 783, 813, and 843 K, during 7.2, 14.4, and 21.6 ks. Other significant parameters were left unchanged, such as pressure (400 Pa), and gas flow (4x10 -6 m 3 /s). The samples were characterized according to the thickness and phases present in the nitrided layer, by optical and scanning electronic microscopy (SEM), and X-ray diffraction (XRD). The microhardness profiles were also obtained. Finally, the corrosion rate of the samples was measured using the potentiodynamic polarization method. The contour plots of the resulting response surfaces are presented herein.

The purpose of this study was to examine the mechanical behaviour of orthodontic delta retraction springs. Twelve titanium-molybdenum (0.016 × 0.022 inch) delta loops were studied. The springs were analysed by means of the finite element (FE) method and experimental tests using a platform transducer. Each spring was activated from 0 to 6 mm. Statistical analysis of the data was carried out by one-way analysis of variance and Games-Howell parametric multiple comparison test for heterogeneous variances. FE analysis revealed that the stress level varied from 277 to 1273 MPa. At 6.1 mm (773 MPa), the springs were still in the elastic range. Force levels varied from 0.1 N (10 g) to 2.2 N (224 g) at 1.4-8.1 mm of activation for the numerical study and from 0.44 N (45 g) at 1 mm to 2.02 N (206 g) at 6 mm of activation in the experimental study. The spring rate was within the levels that are appropriate for clinical use (34 g/mm). Vertical forces (Fy) showed constancy and were of low magnitude. The anterior moment/force ratio from the experimental tests was 14 at 3 mm of activation decreasing to 10.7, 8.7, and 7.2, for 4, 5, and 6 mm of activation, respectively. The springs could be activated up to 7 mm without exceeding the elastic limit.